The present invention relates to the display of acquired signal data, and more particularly to a mixed signal display for a measurement instrument that shows both analog and logic signal waveforms using a “no dead time” data acquisition architecture.
In mixed signal measurement instruments analog signals are digitized and logic signals are sampled. In older instruments the digitization rate of the analog signals often matched the sample rate of the logic signals. When the digitization rate became fast enough relative to the analog signal channel bandwidth, it became possible to interpolate the digitized analog signal data so that continuous analog waveforms could be drawn on a display screen even when the display resolution is greater than the resolution of the digitized analog signal data. Since it is not possible to interpolate the sampled logic signal data, hardware was developed to sample the logic signals at rates much higher than a system clock. Such hardware is currently being used in logic analyzers to implement a MagnIVU™ acquisition system as found in the TLA Series of logic analyzers manufactured by Tektronix, Inc. of Beaverton, Oreg.—see U.S. Pat. No. 5,526,286 entitled “Oversampled Logic Analyzer.”
The measurement instruments store the acquired analog and/or logic signal data in an acquisition memory. Concurrently a trigger system observes one or more input signal channels to detect trigger events. During a pre-trigger time data is stored in the acquisition memory, but trigger events detected by the trigger system are ignored. After the pre-trigger data is stored a detected trigger event starts a post-trigger time during which data continues to be stored in the acquisition memory. Once the post-trigger time starts, additional detected trigger events are ignored. At the end of the post-trigger time writing of data into the acquisition memory is halted. The digitized analog signal data and/or sampled logic signal data are then read from the acquisition memory and waveform images are drawn in a display buffer. Trigger events continue to be ignored until the data has been read from the acquisition memory, a new acquisition started and the next pre-trigger time has elapsed.
It is desirable in a mixed signal measurement instrument to be able to display all of the trigger events. As shown in co-pending U.S. patent application Ser. No. 11/388,428 entitled “No Dead Time Data Acquisition”, the basic idea behind a “no dead time” data acquisition of an analog signal is an architecture that allows all trigger events to be shown on a display.
What is desired is the ability in a no dead time data acquisition architecture to also draw logic signals together with analog signals for display at the same high rate.